Lecture 2 - Functional properties of skeletal muscle 2 Flashcards
What gives us the capability to vary the strength of contraction?
the varying number f Motor units recruited at any time
Varying the frequency of contraction of individual MUs
What is the physiology of Fast-fatigueable (FF) MU type?
Type IIX
fast contracting
relax very qucikly
repeated stimulation produces force quickly but will fatigue
ely on glycolysis
poor capillarisation
What is the physiology of S (slow) MU type?
Type I
rely upon oxidation
rich capillarisation
slow contraction, slow relaxation
fatigue - can sustain force over time, more resistant to fatigue
What is the physiology of Fast- fatigue resistant (FR) MU type?
Type IIA
rely on both types of metabolism
properties lie in the middle of the FF and S types
What are the fastest contracting fibres in humans?
Type IIX
A given level of excitatory input will produce more depolarisation of the ______ axons becasue of their …
A given level of excitatory input will produce more depolarisation of the smallest axons becasue of their smaller membrane areas
First axons to fire will be those of the smallest MUs
Any task recruits the slow MUs first, then as the task intensity increases…
Larger MUs
What do muscle spindles sense?
the lengths of the muscle fibres during contraction
Golgi tendon organs are..
designed to sense the forces developed by the fibre
The centres of the intrafusal fibres are not ______but their ends do contain fibres that contract when stimulated by ____-motor neurons
The centres of the intrafusal fibres are not contractile but their ends do contain fibres that contract when stimulated by gamma-motor neurons
extrafusal (“ordinary”) muscle fibres are innervated by..
alpha-motor neurons
The sensory neurons that wrap around the centre of the spindle are …
tonically active
they fire A.Ps when the muscle is at resting length
these signals travel to the spinal cod where the afferent spindle synapses with the alpha-MN
The alpha-MN create tonic excitation and contraction in the extrafusal fibres associated with the muscle spindle meaning…
even at “rest” a muscle maintains a certain degree of tension or tone
How is spindle length maintained during contraction?
Gamma-motor neurons innervate the ends of the intrafusal fibres which then contract
maintaining stretch on the sensory nerve endings, counteracts the release of tension on the spindle
Therefore, when the extrafusal fibres shorten during contraction, the intrafusal fibres remain stretched and continue to monitor tension in the muscle
What does activation of Golgi tendon organ (GTO) cause?
inhibition of a-MN and decreases muscle contraction
slows muscle contraction as the force of contraction increases
